The present invention relates to the attachment of semiconductor devices and the like to an electronic substrate and, more particularly, relates to the temporary attachment of semiconductor devices and the like to an electronic substrate for testing and burn-in.
The method of attaching semiconductor devices to an electronic substrate, for example a ceramic material, by controlled collapse chip connection (C4), also known as flip chip attach, is well known in the art. In the C4 method, an array of solder balls is formed on the surface of the semiconductor device. The solder balls are typically composed of high melting point solder, for example 97 weight % lead, 3 weight percent tin (97/3), at an approximate pitch of 10 mils. The solder is reflowed at a temperature of about 350.degree. C. to join the semiconductor device to the electronic substrate. There can be one semiconductor device per electronic substrate, known as a single-chip module (SCM), or multiple semiconductor devices per electronic substrate, known as a multi-chip module (MCM).
After manufacture of the semiconductor devices, they are tested for electrical continuity. More recently, semiconductor devices undergo "burn-in" which is the preliminary operation of the semiconductor device to detect early failure of the functioning of the semiconductor device. There is a growing need in the microelectronics industry for known good die (KGD), which are semiconductor devices that have been tested and burned-in and are known to be good prior to sale or installation. It is also desirable that semiconductor devices used to populate an MCM be known to be good prior to being placed on the MCM, so that it is not necessary to reflow the MCM several times to replace semiconductor devices that may be bad.
In order to produce KGD, one method is to test the semiconductor device on a ceramic carrier to which the KGD has been soldered. The carrier, or electronic substrate, can be a standard single-chip carrier, which enables the semiconductor device to be tested and burned-in. A key attribute of this process should be the ability to remove the semiconductor device from the electronic substrate without damaging the semiconductor device or the C4 solder balls on the semiconductor device, so that the semiconductor device can be used in its final application. It is a simple matter to mount a semiconductor device on a conventional electronic substrate by the C4 connection method and test and burn-in the semiconductor device. However, the matter is complicated when removal of the semiconductor device is attempted without damaging the C4 solder bumps on the semiconductor device so that the semiconductor device may be used on another electronic substrate.
Today, this problem has been addressed by using a ceramic electronic substrate with reduced solderable pads on the top surface of the electronic substrate. Using a C4 pad on the electronic substrate which is approximately 1.5 mils in diameter, as opposed to the standard pad size of 5.5 mils, enables a semiconductor device to be joined to the electronic substrate by reflow of the C-4 solder balls, tested, burned-in and subsequently cold-sheared off of the electronic substrate. The effectiveness of this solution requires a reduced area solderable connection on the electronic substrate.
Aimi et al. U.S. Pat. . 5,237,269, the disclosure of which is incorporated by reference herein, provides a reduced area solderable connection on the electronic substrate by masking the solderable area with an overlay which is made of a non-wettable material to which solder will not adhere. Holes are provided in the overlay such that a restricted connection may be made between the C-4 solder balls and the underlying solderable area of the electronic substrate. After testing, the C-4 solder balls are sheared from the electronic substrate and then reflowed to reshape them for subsequent use.
Various solutions have been proposed for joining semiconductor devices to electronic substrates. Chong et al. U.S. Pat. No. 5,535,936, the disclosure of which is incorporated by reference herein, discloses a method of applying low temperature solder in a fine pitch pattern on a printed circuit board for the purpose of attaching (permanently apparently) a semiconductor device to a printed circuit board. As noted at column 2, lines 18-22, approximately 20-80 cubic mils of solder are needed on the printed circuit board for a reliable joint.
Tsukada U.S. Pat. No. 5,488,200, the disclosure of which is incorporated by reference herein, discloses a method for reusing SCM or MCM substrates by end milling the chips and underfill off the top surface of the substrate and establishing a planar surface of residual C4 solder to which a new chip can be joined using low temperature solder.
Baker U.S. Pat. No. 4,739,917, the disclosure of which is incorporated by reference herein, discloses high temperature solder mounds deposited on conductive pads on the substrate which function only as mechanical guides for the various lead configurations of the components. Then, low temperature solder is deposited and reflowed over the mechanically anchored high temperature mounds and component leads to make the joint.
It would be desirable to be able to have a process for temporary attachment of the semiconductor device to an electronic substrate for use in test and burn-in, and subsequent removal of the semiconductor device without damaging the C4 solder balls on the semiconductor device, which is low cost and easily manufacturable.
Accordingly, it is a purpose of the present invention to have a process for temporary attachment of the semiconductor device to an electronic substrate for use in test and burn-in, and subsequent removal of the semiconductor device without damaging the C4 solder balls on the semiconductor device.
It is another purpose of the present invention to have such a process which is relatively low cost and easily manufacturable.
It is yet another purpose of the present invention to have an article for the temporary attachment of the semiconductor device to an electronic substrate for use in test and burn-in, and subsequent removal of the semiconductor device without damaging the C4 solder balls on the semiconductor device.
These and other purposes of the present invention will become more apparent after referring to the following description considered in conjunction with the accompanying drawings.